The project is concerned with the modulation of the startle reflex pattern in animals and man. There are four goals of the project: to identify stimulus conditions which provide phasic and tonic control over reflex facilitation and inhibition; to understand the part played by higher mental processes in controlling reflex behavior; to explore the relationship between physiological processes and reflex regulation; and to develop the reflex paradigm for use in the clinical assessment of sensory deficits. The experimental procedures involve elicitation of acoustic and tactile startle reactions by intense auditory stimuli, weak peripheral electrical shock, and air puffs, recording whole body flexion or eye- blinks responses. These reflexes are facilitated or inhibited, by an order of magnitude, by coincident neutral or irrelevant stimuli of appropriate intensity and time of application. The experiments will explore the roles of cognitive and emotional processes in these effects, and physiological mechanisms, in cortex, reticular formation, and cerebellum. The sensitivity of reflex modulation to small sensory disturbances will be explored, to determine the value of these procedures for clinical diagnosis.